Hepatitis C virus (HCV) belongs to the family Flaviviridae and is a virus having a single stranded (+) sense RNA genome and is known to cause hepatitis C.
HCV causes chronic hepatitis by persistent infection. Currently, the main cause of chronic hepatitis observed worldwide is persistent HCV infection. Actually, around 50% of individuals with persistent infection develop chronic hepatitis. Chronic hepatitis in approximately 20% of these patients shifts to liver cirrhosis over the course of 10 to 20 years, and some of these patients further go on to advanced lethal pathological conditions such as hepatic cancer.
Hepatitis C is currently treated mainly by a therapy using interferon-α or interferon-β, or a therapy using a combination of interferon-α and ribavirin, a purine-nucleoside derivative. However, even when these therapies are performed, the therapeutic effects are observed in only approximately 60% of all treated patients. When therapies are ceased after effects are seen, the disease recrudesces in more than half of the patients.
It is an important goal to develop therapeutic agents or prophylactic agents effective against hepatitis C. The incidence rate of hepatitis C, which in the end brings about serious consequences, is high in industrial countries, and there is currently no causal treatment available. Hence, the development of HCV-specific chemotherapies and vaccine therapies are desired. A target for the development of an anti-HCV agent may be the suppression of HCV replication or the suppression of infection of cells with HCV.
Recently, HCV subgenomic RNA replicon systems have been prepared as HCV-derived autonomously replicable RNA (see, Patent Documents 1, 2 and 3, Non-Patent Documents 1-4). In the HCV subgenomic RNA replicon systems, HCV replicon RNA in which the structural genes of the HCV genome is eliminated and replaced with a drug-selectable marker gene, are prepared and introduced into cultured cells, and thereby the replicon RNA is replicated autonomously in the cells. By using these systems it becomes possible to analyze the replication mechanism of HCV. However, this is an experimental system in which only viral RNA replication is evaluated in the process of the proliferation and replication of HCV virus, and the process of the formation of HCV virus particles in the infected cells and the extracellular release or infection to another cell cannot be analyzed.
At this time, the process of HCV virus particle formation and extracellular release as well as infection to another cell can only be evaluated in the experimental systems using animals such as chimpanzees (Non-Patent Document 5). However, the experimental systems using living organisms such as animals are complicated and very difficult to analyze. Therefore, in order to analyze the process of HCV virus particle formation and extracellular release as well as infection to another cell, and to produce an anti-HCV agent which will have the action mechanism of inhibiting this process, it is necessary to establish a highly simplified experimental system reproducing this process, i.e. a HCV virus particle production system in cell culture experimental systems.
Further, once HCV virus particles can be provided stably using the cell culture system, it is possible to attenuate the virus or to produce noninfectious HCV virus using molecular biological techniques, and this can be used in vaccines.    Patent Document 1: JP Patent Publication (Kokai) No. 2001-17187    Patent Document 2: International Patent Application PCT/JP03/15038    Patent Document 3: JP Patent Application No. 2003-329082    Non-Patent Document 1: Lohmann et al., Science, (1999) 285, p. 110-113    Non-Patent Document 2: Blight et al., Science, (2000) 290, p. 1972-1974    Non-Patent Document 3: Friebe et al., J. Virol., (2001) 75(24): p. 12047-12057    Non-Patent Document 4: Ikeda et al., J. Virol., (2002) 76(6): p. 2997-3006    Non-Patent Document 5: Kolykhalov et al., Science, (1997) 277, p. 570-574    Non-Patent Document 6: Kato et al., Gastroenterology, (2003) 125, p. 1808-1817    Non-Patent Document 7: Yanagi et al., Proc. Natl. Acad. Sci., (1997) 96(16): p. 8738-8743    Non-Patent Document 8: Okamoto et al., J. Gen. Virol., (1991) 73, p 2697-26704    Non-Patent Document 9: Aoyagi et al., J. Clin. Microbiol., (1999) 37(6): p. 1802-1808